The "circle of Willis," attributed to the 17th century Sedleian professor of natural philosophy at Oxford and one of the founders of the Royal Society, is not a true circle, but a seven-sided structure, a heptagon. Nor was Willis, the illustrious scholar and physician, the first to describe the arterial channels at the base of the brain. The published works of Casserio appearing in 1627, Vesling (1653), Fallopius (1561), and Wepfer (1658) either described or illustrated incompletely the vascular network.1 Willis never claimed priority, although he was the first to combine a complete description with an equally complete illustration. He attributed its significance in health and disease to the assurance of an adequate blood supply to what was recognized at that time as the organ of thought.
Thomas was born at Great Bedwin in Wiltshire, the son of a farmer and retainer of St. John's College, who lost his